The present invention relates to air filtration systems and more particularly to control valves or dampers for adjusting the flow of air through filters of a clean room.
Clean rooms provide a controlled, contaminate free work area necessary for many manufacturing, medical and research operations. Typical clean rooms include a plenum above a bank of high efficiency filters or a plurality of diffuser units supported in a ceiling structure. A blower introduces air under pressure to the plenum above the filters or to the individual diffuser units. The air is forced through the filters and passes vertically downwardly into the room. Return ducts are provided in or adjacent a floor to recirculate the air to the blower.
A clean room has a higher pressure than the pressure around the room or adjacent the room's exterior. This pressure gradient forces contaminants out of the room. Air flow is regulated in part by dampers or air flow control valves positioned adjacent the filters or in the diffuser units. Accurate control of the air flow is necessary to maintain the desired flow rates and pressure gradients.
With most clean room systems, a large volume of air is transferred and relatively high air flow rates are experienced. Heretofore, pivoting or sliding vanes or louvers have been provided to block air passage through the filters. With such valves, metal-to-metal contact permits leakage and inefficiency. This leakage may also cause undesirable whistling and vibration.
Examples of clean room systems and prior filter systems may be found in U.S. Pat. Nos. 3,522,724 entitled METHOD AND APPARATUS FOR TESTING CLEAN ROOM FILTRATION EFFICIENCY and issued on Aug. 4, 1970, to Knab; 3,780,503 entitled LOW PROFILE FILTER SYSTEM and issued on Dec. 25, 1973, to Smith; and 3,986,850 entitled FLOW CONTROL APPARATUS AND AIR FILTERS and issued on Oct. 19, 1976, to Wilcox. The Smith and Wilcox patents both disclose filter systems having sliding plate valves. In the Smith system, a fixed plate defining a plurality of apertures is secured to a filter frame above a high efficiency filter. A movable plate also defining a plurality of apertures is slidably positioned on the fixed plate. A cam arrangement, accessible from the downstream side of the filter, adjusts the relative positioning of the two plates. The apertures are moved into and out of alignment to adjust the air flow.
In the Wilcox sliding plate valve, a highly viscous, nonevaporating fluid is positioned between the two plates to prevent cross flow or lateral flow of air between the plates. The fluid may be a household petrolatum or a silicone grease. The nonevaporating fluid must be evenly applied between the plates for proper operation.
A need exists for an air flow control valve or damper adapted for use in clean room systems which permits accurate adjustment of flow without cross flow or leakage and which is more easily manufactured at reduced costs when compared to prior approaches. A need further exists for a damper which will reduce or attenuate the noise associated with the high flow and volume rates found in the typical clean room.